It is unlikely you can put enough pressure on a slide with a universal sight pusher clamp to damage the slide.
But it is even more unlikely a 'universal sight pusher' will fit more then one or maybe two brands of guns properly, so damage is possible.
You should have bought a dollar two ninety eight brass punch and a small hammer.
Thats worked for me on everything including night sights, for 50 years in the shop.
When I am forced to clamp a slide real tight in a drill or mill vice?
I machine a brass or steel filler block to support the slide rails from the inside first.
rc